1. Field of the Invention
The present invention relates to an optical fiber array in which an optical fiber, a bundle of optical fibers or an optical fiber ribbon is attached and fixed on an array substrate and which is useful for connecting an optical fiber or an optical fiber ribbon to optical components or a planar light wave circuit (PLC).
2. Description of the Related Art
In an optical fiber communication system, an optical fiber array is employed to connect an optical fiber to optical components or PLC. The optical fiber array usually comprises an array substrate provided with V-grooves, each V-groove being for positioning an end portion of an optical fiber, and a lid for pressing the end portion of the optical fiber in the V-groove. The optical fiber includes an optical fiber and an optical fiber ribbon in which a plurality of optical fibers are integrally bundled with a tape or resin. The optical fiber array is manufactured by positioning the end portion of the optical fiber in the V-groove, pressing the end portion of the optical fiber in the V-groove with the lid, bonding the optical fiber on the array substrate, using the adhesives, and then polishing the front end portion of the array substrate where an end face of the optical fiber is exposed.
In recent years, an optical fiber is required to connect to a PLC (PLCs) having a mode field diameter (a smaller mode field diameter than ITU-T standard size) different from a standard single mode optical fiber. In this case, an optical fiber having a small mode field diameter is employed for connection with the PLC, and an optical fiber having a standard mode field diameter is employed for connection with a cable side. In the optical fiber array for use to make connection with the PLC, the optical fiber having the smaller mode field diameter is fusion spliced at a top end of the optical fiber having the standard mode field diameter, causing a large splice loss.
In splicing a non-standard optical fiber and the standard single mode optical fiber which have different mode field diameters, it is difficult to obtain a practical splice loss only by normal fusion splicing technique. Conventionally, a method is known in which optical fibers are fusion spliced and then a spliced portion of the optical fibers is additionally heated (Thermally Expanded Core, hereinafter referred to as TEC or TEC process) to reduce the splice loss (e.g., refer to JP2618500 and JP-A-2000-275470). With such an additional heating, a dopant added to the core portion of the optical fiber is thermally diffused to the cladding portion of the optical fiber to cause an expand of the mode field diameter locally. Thus, the mode field diameters of the optical fibers at the spliced portion are coincident with each other.